This is a proposal to develop and apply a unique and powerful new gene transfer strategy for specific immunotherapy of myasthenia gravis (MG). Ideally, therapy of MG should specifically inhibit the autoimmune response to the autoantigen, acetylcholine receptor (AChR), without otherwise interfering with the immune system. Because the antibody response to AChR is T cell dependant, elimination of the AChR-specific T cells interrupts the autoimmune disorder at a pivotal point, resulting in clinical benefit. This requires elimination of virtually all AChR-specific T cells. However, the marked heterogeneity of T cell responses to AChR in humans and in experimental animals presents a challenge in designing specific treatment capable of eliminating the entire repertoire of AChR-specific T cells. The investigator's targeting strategy is based on the fact that a myasthenic individual's own antigen presenting cells (APCs) can present AChR epitopes to that indivudual's entire repertoire of AChR specific T cells. They have adapted a method that induces the APCs to process and present AChR by inserting a cDNA construct that encodes the key immunogenic domain of the AChR flanked by signals that induce the APCs process and present it. These APCs target AChR-specific T cells highly effectively. In order to eliminate the targeted T cells, they utilize Fas ligands as a "warhead." When FasL interacts with Fas, which is abundantly expressed on activated T cells, it induces apoptosis and death of the T cells. Insertion of the gene for FasL in APCs induces them to express FasL, which effectively kills Fas-expressing target cells. It is essential to protect these APCs, which would die by FasL- induced "suicide," because they also express Fas. To protect these APCs, they insert a 3rd gene for a truncated form of FADD, which acts as a dominant negative inhibitor of Fas-mediated cell death, into the APCs. To insert all 3 genes simultaneously into APCs ex vivo, they have developed a vaccinia virus vector (vvv), which carries all 3 genes. This vaccinia vector can transfer multiple genes simultaneously, inducing high level production of the gene encoded proteins. When it is attenuated (by treatment with psoralen and UV light) the vvv does not replicate but does direct expression of the gene products. Finally, the expression of FasL directed by their vvv system should confer protection against an immune attack by the host's immune system on the virus vector itself. They now propose to optimize the system and develop it in two animal models: (1) experimental MG, including a new transgenic myasthenic mouse model; and (2) a transgenic mouse model of hemaglutinin (HA) sensitivity. The experiments described in the present proposal will develop this novel strategy in experimental animals, both for prevention and for treatment of EAMG. This method is designed to be suitable for treatment of human autoimmune diseases. When optimized in experimental animals, it will be adaptable for treatment of patients with MG and other autoimmune diseases.